linux-kernel - Re: [PATCH v3 04/19] mm: slub: implement SLUB version of obj_to

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Message-ID: <88972cc2-2120-4257-ae8d-141e014c54e4@suse.cz>
Date:   Wed, 20 May 2020 11:51:51 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Roman Gushchin <guro@...com>, Christopher Lameter <cl@...ux.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>, linux-mm@...ck.org,
        kernel-team@...com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 04/19] mm: slub: implement SLUB version of
 obj_to_index()

On 5/13/20 2:57 AM, Roman Gushchin wrote:
> 
> Btw, I'm trying to build up a prototype with an embedded memcg pointer,
> but it seems to be way more tricky than I thought. It requires changes to
> shrinkers (as they rely on getting the memcg pointer by an arbitrary
> kernel address, not necessarily aligned to the head of slab allocation),
> figuring out cache merging, adding SLAB support, natural alignment of
> kmallocs etc.

Is the natural alignment of kmallocs a problem right now? As kmalloc()
allocations are AFAIK not kmemcg-accounted? Or does your implementation add
memcg awareness to everything, even if non-__GFP_ACCOUNT allocations just get a
root memcg pointer?

> Figuring out all these details will likely take several weeks, so the whole
> thing will be delayed for one-two major releases (in the best case). Given that
> the current implementation saves ~40% of slab memory, I think there is some value
> in delivering it as it is. So I wonder if the idea of embedding the pointer
> should be considered a blocker, or it can be implemented of top of the proposed
> code (given it's not a user-facing api or something like this)?
> 
> Thanks!
>